Highly Flexible Polylactide Food Packaging Plasticized with Nontoxic, Biosourced Glycerol Plasticizers

Abstract

Polylactide (PLA) is a promising biosourced and biodegradable polymer substitute for traditional petroleum-based products. Despite its recognized potential, its widespread adoption is restricted by its brittleness and low ductility and, thus, to enhance its material properties, plasticizers must be blended with PLA to lower the glass transition temperature (T g) and impart flexibility into the blend. As such, this work focused on the synthesis of a family of biosourced plasticizers for applications in flexible food packaging using glycerol, succinic anhydride, and alcohols of varying chain lengths. The effect of the chemical structure on plasticization performance, migration, blend morphology, and toxicity was evaluated and compared to the commercial plasticizer acetyl tributyl citrate. Plasticizer/PLA blends were prepared using solvent-casting as well as melt-mixing to produce thin films and bulk specimens. At loadings of 20 wt %, improved flexibility (up to 435% elongation) was observed in films with the glycerol plasticizers relative to neat PLA (6% elongation), while T g’s were reduced by up to 45 °C from that of neat PLA (T g ∼ 60 °C). Phase morphologies evaluated with scanning electron microscopy showed good incorporation of the plasticizers into the PLA matrix. Leaching behavior of the plasticized blends was evaluated in different food simulants and showed that plasticizers composed of branched or longer alkyl chains produced two- to sixfold lower migration rates compared to those with short alkyl chains. Finally, plasticizer candidates were shown to be nontoxic and did not impact HepG2 cell viability over a period of 7 days in an in vitro mammalian cell assay.

Bio‐based glycerol plasticizers for flexible poly(vinyl chloride) blends

“…In addition to evaluating the thermal and mechanical properties of the plasticizers in PVC blends, we aimed to investigate their toxicity through an in vitro mammalian cell assay. It was previously shown via an in vitro cytotoxicity assay that the glycerol compounds functionalized with linear chains of six carbons or less are nontoxic, whereas the longer chain or branched analogs showed mild levels of toxicity over a seven‐day period 32 . Here, we also evaluated two widely used phthalate‐based plasticizers for their cytotoxicity–di(2‐ethylhexyl) phthalate (DEHP) and DOTP.…”

“…The cell‐counting kit‐8 (CCK‐8) was purchased from Cedarlane Laboratories Ltd (Burlington, ON). The glycerol plasticizers used in this study were synthesized in accordance with a previously reported procedure 32 …”

“…The glycerol plasticizers used in this study were synthesized in accordance with a previously reported procedure. 32…”

“…Glycerol is an ideal starting material for the design of consumer items, such as plasticizers, as it is both nontoxic and contains three hydroxyl groups which can be exploited for further synthetic transformations 31 . As such, a series of bio‐based glycerol compounds were recently developed and shown to be effective plasticizers to produce highly flexible polylactide (PLA) materials with improved mechanical toughness 32 . In addition to improving the mechanical properties of PLA, a facile two‐step synthetic route was developed to prepare the plasticizers thereby limiting the use of organic solvent while only generating water as a by‐product.…”

“…31 As such, a series of bio-based glycerol compounds were recently developed and shown to be effective plasticizers to produce highly flexible polylactide (PLA) materials with improved mechanical toughness. 32 In addition to improving the mechanical properties of PLA, a facile twostep synthetic route was developed to prepare the plasticizers thereby limiting the use of organic solvent while only generating water as a by-product. Furthermore, the compounds were shown to be nontoxic through an in vitro cytotoxicity assay.…”